This invention relates to acrylic toughened cyanoacrylate compositions.
Cyanoacrylate compositions are well known as adhesives for a variety of substrates. However, traditional cyanoacrylate-based adhesives tend to be brittle after cure. A variety of additives and fillers have been added to cyanoacrylate adhesive compositions to improve its toughness.
U.S. Pat. No. 3,183,217 to Serniuk et al. discloses free radical polymerization of a methacrylic acid or methyl methacrylate monomer with a non-polar or mildly polar olefin where the monomer is completed with a Friedel-Crafts halide. Also disclosed is the polymerization of acrylonitrile and various olefins.
U.S. Pat. No. 3,963,772 to Takeshita discloses liquid telomers of alkylene and acrylic monomers which result in short chain alternating copolymers substantially terminated at one end of the polymer chains with the more reactive alkylene units. The liquid telomers are useful in making elastomeric polymers for high molecular weight rubbers which permit the ready incorporation of fillers, additives, and the like, due to its liquid phase.
U.S. Pat. No. 4,440,910 to O""Connor is directed to cyanoacrylate compositions having improved toughness, achieved through the addition of elastomers, i.e., acrylic rubbers. These rubbers are either (i) homopolymers of alkyl esters of acrylic acid; (ii) copolymers of another polymerizable monomer, such as lower alkenes, with an alkyl ester of acrylic acid or with an alkoxy ester of acrylic acid; (iii) copolymers of alkyl esters of acrylic acid; (iv) copolymers of alkoxy esters of acrylic acid; and (v) mixtures thereof.
U.S. Pat. No. 4,560,723 to Millet et al. discloses a cyanoacrylate adhesive composition containing a toughening agent comprising a core-shell polymer and a sustainer comprising an organic compound containing one or more unsubstituted or substituted aryl groups. The sustainer is reported to improve retention of toughness after heat aging of cured bonds of the adhesive. The core-shell polymer is treated with an acid wash to remove any polymerization-causing impurities such as salts, soaps or other nucleophilic species left over from the core-shell polymer manufacturing process.
U.S. Pat. No. 5,340,873 to Mitry discloses a cyanoacrylate adhesive composition having improved toughness by including an effective toughening amount of a polyester polymer derived from a dibasic aliphatic or aromatic carboxylic acid and a glycol.
U.S. Pat. No. 5,994,464 to Ohsawa et al. discloses a cyanoacrylate adhesive composition containing a cyanoacrylate monomer, an elastomer miscible or compatible with the cyanoacrylate monomer, and a core-shell polymer being compatible, but not miscible, with the cyanoacrylate monomer.
The known toughening agents mentioned above generate or contain acid impurities which can cause hydrolysis of the cyanoacrylate monomer, forming carboxylic acids which drastically retard cure speed, contribute to a rapid deterioration in adhesive performance, and require high concentrations of stabilizers. Toughening agents such as core shell polymers have been shown to be inconsistent in performance and can be difficult to formulate.
Thus, it would be desirable to provide a toughening agent for cyanoacrylate compositions which has reduced acid generation such that cure speeds and consistent adhesive performance are not inhibited, easy to formulate, and use lower concentrations of stabilizers.
The present invention is directed to, in a first aspect, a cyanoacrylate composition which demonstrates enhanced toughness and faster fixturing speeds including: a cyanoacrylate component; and a toughening agent including one or more acrylic monomers. Preferably, the one or more acrylic monomer(s) are monofunctional, although not limited to such, and include methyl methacrylate, butyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, and combinations thereof, and may be present in an amount of about 1% by weight to about 5% by weight of the composition. Most preferred acrylic monomers include butyl acrylate monomers, isobornyl acrylate monomers, methyl methacrylate monomers, a combination of methyl methacrylate and butyl acrylate monomers, or a combination of isobornyl acrylate and methyl methacrylate.
In another aspect, the present invention is directed to a cyanoacrylate composition which demonstrates enhanced toughness including: a cyanoacrylate component; an acrylic monomer toughening agent; and one or more additives selected from the group consisting of plasticizers, accelerators, fillers, opacifiers, thickeners, viscosity modifiers, inhibitors, thixotrophy conferring agents, stabilizers, dyes, thermal degradation enhancers, and combinations thereof, where upon cure, the cyanoacrylate composition has an average tensile shear strength of over 4400 psi after curing at room temperature for 72 hours and 2 hours post cure at 121xc2x0 C.
In yet another aspect, the present invention is directed to cyanoacrylate adhesive composition including about 75% to 98% by weight of a cyanoacrylate component based on a total weight of the composition; about 1% to about 10% by weight of an acrylic monomer toughening agent, the acrylic monomer being selected from butyl acrylate, isobornyl acrylate, methyl. methacrylate, and combinations thereof; and one or more additives selected from the group consisting of accelerators, fillers, opacifiers, thickeners, viscosity modifiers, inhibitors, thixotrophy conferring agents, stabilizers, and combinations thereof.
In still yet another aspect, the present invention is directed to a method of bonding two or more substrates including the steps of: providing at least two substrates; dispensing, on at least a portion of a surface of one or both of the at least two substrates, a cyanoacrylate adhesive composition including: a cyanoacrylate component; and a toughening agent including one or more acrylic monomers; contacting the surfaces of the at least two substrates having the cyanoacrylate adhesive composition thereon; and curing the cyanoacrylate adhesive composition.
In an additional aspect, the present invention is directed to a bonded assembly including: a first substrate having a first surface; another substrate having a second surface; and a cured cyanoacrylate adhesive composition disposed between the first and second surfaces, the composition having included prior to cure: a cyanoacrylate component; and a toughening agent selected from butyl acrylate, isobornyl acrylate, methyl methacrylate, or combinations thereof. Once cured, the toughening agent is copolymerized with the cyanoacrylate component. Preferably, the peel strength of the composition is greater than about 6 pounds/inch after room temperature cure of about 72 hours. Preferably, the tensile shear strength of the composition is greater than about 4400 psi after 72 hours at room temperature and 2 hours post cure at 121 xc2x0 C.